Formation of huge cyclic oligomers in the condensation polymerization of bis(9-hydroxy-1,4,7-trioxanonyl) substituted naphthalene and benzenes with both aromatic and aliphatic bis-acid chlorides

Abstract

Without the use of high dilution techniques condensation polymerization of bis(9-hydroxy-1,4,7-trioxanonyl) substituted naphthalene and benzenes (1a–d) with the bis-acid chlorides terephthaloyl dichloride (2), adipoyl dichloride (5a) and isophthaloyl dichloride (5b) at 80 °C, respectively, gives giant-size macrocycles, i.e. crownophanes 3a(n) with n = 1–5, 3b–d(n) with n = 1–3 and 6a–b(n) with n = 1–2, respectively, in high overall yield (ca. 30% w/w, monomer conc. 0.033 M). The crownophanes with 28–150 atom perimeters have been isolated using preparative column chromatography. Both in the melt and in solution, with a ten-fold increase in monomer conc. (0.33 M), cyclic oligomer yields remain considerable (melt, ca. 2% w/w, and solution ca. 10% w/w). ¹H NMR conformational analysis of the 9-hydroxy-1,4,7-trioxanonyl side chains of both 1a and 1d at 25 and 80 °C have shown that all HO–[CH(I)₂–CH(II)₂–O]_n– units are almost exclusively present in their gauche conformation at both temperatures. This is supported by semi-empirical AM1 calculations. Hence, favourable pre-orientation of the side chains is apparently an important factor in the formation of cyclic oligomers. Single crystal X-ray structures of 3a(1), 3d(1) and 6a(1) are reported; solid-state packing motifs are strongly affected by the type of diol and bis-acid constituent.